61th Meeting of the ILL Scientific Council
21-22 october 1999
Item 9 of the agenda
Science Council Review of ILL Powder Diffraction Instruments
CONTENTS
Summary and Conclusions - Recommendations
1. General presentation of the instruments
a - Historical
b - Present situation of the 5 instruments
c - Staff
2. Statistics
a - Experimental request and realization
b - Publications
3. Users
a - General characteristics of the user community
b - User Survey
4. Science
a - General
b - Evolution of subjects and scientific areas for future
5. Instrumentation
a - Microstrip detectors
b - The high precision Strain Scanner project
c - Super-D2B
d - Data acquisition and software
6. Comparison with other neutron and with synchrotron instruments
a - Comparison with other constant wavelength neutron diffractometers
b - Comparison with Time-of-Flight instruments
c - Neutrons versus Synchrotron Radiation in Powder Diffraction
7. Conclusion : the powder diffraction instrument profile of ILL
Appendix 1 : Programme of the Workshop
Appendix 2 : Questionnaire on Powder Diffraction Instrument Review
Appendix 3 : Highlights and impact of ILL publications
Appendix 4 : Statistics on experiments, publications and users
Summary and Conclusions - Recommendations
This second review of ILL instruments covers 5 machines : D2B (high resolution powder diffractometer), D20 (high flux powder diffractometer), D4 (diffractometer for liquids), D1A (high resolution diffractometer, now mainly used for strain scanning) and the CRG-B D1B (high flux, equipped with a position sensitive multidetector).
The aim of the review was to examine the science performed on these instruments, to survey the user community, to prospect on future scientific developments, to compare the above ILL instruments with other neutron and X-ray powder diffractometers, and to establish the priorities for instrumental improvements.
For this purpose, we have :
- prepared statistical informations and performed a bibliographic review, including a list of highlights and a measurement of the impact of publications (found in Appendix 3);
- performed a User's Survey (summarized in Appendix 2);
- organized a two-days meeting which was held in Grenoble on 22-23 march 1999. The programme of the meeting is given in Appendix 1. They were 51 participants to the workshop, coming from UK (16, including 6 from ISIS), France (12, including 2 from LLB), Germany (2), Italy (3), Switzerland (2), Spain (1), Sweden (1), Australia (1), ILL (10), ESRF (3). 16 non-ILL speakers presented the science they performed in various fields with neutron scattering (in comparison or complementarity to other techniques), compared the performance of the ILL instruments with those of other (present or future) neutron sources, discussed future needs and made recommendations about instrumental priorities.
D2B is mostly involved in the detailed study of crystalline and magnetic structures, and their dependence with temperature, pressure, etc..., by high resolution Rietveld refinements. It receives a considerable number of users ( 80 experiments per year). Some of the major highlights of ILL were obtained on D2B, on the structures of high TC cuprates and of GMR perovskites.
D20 has been
recently equipped with a large new type of position sensitive
detector ("microstrip" technology), making it the
fastest powder neutron diffractometer in the world, specially
dedicated to the study of chemical kinetics and very small
samples. Unfortunately, this detector failed after one year
operation. D20 is expected to be repaired in spring 2000.
D4 is devoted to
the determination of local atomic arrangements in simple and
complex liquids and amorphous systems, by scattering of short
wavelength neutrons. This instrument is 50 % scheduled (it shares
a hot beam tube with IN1). Its great stability allows the use of
isotopic substitution for precise determination of partial
structure factors.
The two
instruments D1A and D1B were the respective predecessors of the
more performing machines D2B and D20. They are now partially
reconverted. D1A (scheduled 50 %) is largely used for internal
stress studies on materials of technological interest, with the
aim of predicting fatigue threshold and/or validating finite
element models. D1B is since 1997 a french-spanish CRG; its 400-cells
position sensitive detector makes it a multipurpose instrument
for studies of magnetism, phase transitions, textures and
experiments under complex sample environment. D1B has the largest
publication rate of all ILL instruments ( 60 per year).
Scientific
subjects studied by powder diffraction are evolving continuously
and rapidly, and depend of course of the discovery of new
materials. Increasing trends in future will be in situ follow-up
of preparation and kinetics, extreme sample environments, complex
and partially disordered systems, pharmacology, materials for
earth sciences and problems of industrial interest.
Comparison
between ILL powder diffractometers and other instruments was
largely debated during the Workshop. It was emphasized that the
best powder instruments on medium flux sources (LLB-Saclay, SINQ,
and in near future FRM-II) are far from D20 and D2B in intensity,
but owing to the progress in neutron optics, become competitive
with D1A and D1B.
Generally, it was
found that time-of-flight (TOF) and constant wavelength
diffractometers (CWD) are complementary : each type of instrument
has advantages in certain circumstances, and both are often
needed for a full scientific coverage. In particular, D2B and
HRPD have similar resolution and intensity, with some advantages
for D2B at low q and for HRPD at high q. The difficulties on data
treatment for powder diffractometers on spallation sources can
now be overcome by carefull work. TOF instruments are much better
for high pressure structural studies. The commissioning of GEM
and OSIRIS at ISIS might bring new challenge to D20 and D2B. For
liquids, the best neutron instrument will be undoubtly D4C for
some time, because of its exceptional stability.
Neutrons and
synchrotron radiation are found complementary in powder
diffraction. Very generally speaking, if X-rays are better than
neutrons for structure determination, neutrons are better than X-rays
for structure refinement, in particular for obtaining precise
site occupancies and precise atomic positions of light elements
in the presence of heavy elements. Neutrons are of course unique
for magnetic structure determination. Synchrotron radiation is
leading in the field of high pressures. Difficult aspects must be
overcome before one can currently use synchrotron radiation for
strain scanning and for determination of partial structure
factors in liquids by using the anomalous effect.
Taking into
account the great progress mentionned above of instruments on
medium flux reactors and spallation sources, the upgrading of
the ILL powder and liquids diffraction instruments is a priority
to optimize the use of the high flux source.
Concerning the
ILL powder diffraction instrument profile, it was generally
agreed that the minimum required is :
- a "fast"
high intensity instrument for kinetics (with fixed multidetector,
medium / good resolution) : it is now (and it will be) D20;
- a "high
resolution" instrument for Rietveld refinement of structures
: it is now D2B, it should be in the future super-D2B (or a new
instrument) with very high resolution.
They should be
accompanied by two more specialized instruments :
- a diffractometer
for liquids, with fixed short wavelength neutrons : this will be
D4C;
- a high resolution
strain scanner.
D1A and D1B will
still remain usefull instruments for the future, especially for
demanding sample environments.
Summary of
recommendations :
- The repair of D20,
a world leading instrument, is the first priority. It is hoped
that D20 will operate, as planned, in spring 2000.
- The high
resolution instrument D2B must be upgraded in flux and resolution.
The most cost-effective way is the super-D2B project presented
within the Millenium Development Programme, which therefore must
also be given a high priority. But, ILL should also think in a
broader way to what would be the best high resolution instrument
for the future.
- The new high
precision strain scanner project is the third high priority, and
should be realized by ILL even if there were no UK funding.
- A "high
resolution" option should be installed on D20 (focusing Ge
monochromator and high take-off angle).
- ILL should make
an important effort in the field of data acquisition and software,
to improve the software / user interface, and the in situ preliminary
data treatment and immediate visualisation of data.
- ILL should
evaluate what percentage of ILL experiments can be performed at
ILL and nowhere else (i.e. on a medium flux reactor); this number
would be of great interest for ILL to optimize its instrument
suite.
- Even more than
in the case of single crystal diffraction, a determined effort
should be made to increase the user base, in particular among
"non professional" users, and in new fields such as
earth sciences, engineering and industry, pharmacology, etc...
- It would be
important in future, for the study of crystal structures, to have
a joint access to a neutron and a synchrotron radiation
facility.
- ILL should give
more time for short standard (at room temperature, in air) test
or structural characterization powder diffraction experiments,
out of Scientific Councils, and of course make aware the
community of this new procedure.
1. Presentation
of the instruments
a) Historical
At the origin,
ILL was equipped with four "powder" diffractometers : D1A
(high resolution) and D1B (the first position sensitive linear
detector), installed on a thermal neutron guide H22 in the guide
hall; D2 (high flux) on the thermal neutron beam H11 in the
reactor hall, and D4 (liquids) on the "hot" neutron
beam H8 in the reactor hall. At the beginning of the 80's ("Second
Souffle"), it was decided to replace D2 by two instruments :
D2B (high resolution) and D20 (high flux). D2B was commissioned
in 1984, but the construction of D20, which involved the new
"microstrip" technique of position sensitive detectors,
took a long way round. D4 was also upgraded (D4B, with two
position sensitive detectors).
After the ILL
shut-down, the reduction in budget led to transform some
instruments in CRG. This was the case for half of D1A, which was
then managed by the Swiss community up to 1998 (start of the
swiss national source SINQ).
In 1997, when D20
went in operation, D1B was transformed in CRG-B (France + Spain).
b) Present
situation of the 5 instruments
D2B - This
high resolution powder diffractometer (2qFWHM = 0.4°
in the usual high flux mode, 0.1-0.2° in the very high
resolution mode), equipped with a moving set of 64 3He
detectors, is scheduled for many short experiments (more than any
other ILL machine last year). It is mostly devoted to the study
of phase transitions, precise positionning of light atoms,
determination of Debye-Waller factors, by Rietveld refinements. D2B
produced the ILL's most cited publication (in 1990 on charge
transfer in oxide superconductors), and also the most cited ILL
publication since the reactor refurbishment (a 1995 Phys. Rev.
Letters on Giant Magneto-Resistive materials, see highlights § 4a).
An important upgrade (super-D2B project, see § 5c) is foreseen
within the ILL millenium development programme.
D20 - This
machine uses the world's first large-area microstrip position
sensitive detector (1600 cells, Dq = 160°), and can collect
complete diffraction patterns in less than a second, making it
faster than synchrotron machines for many chemical kinetics
experiments (the neutron machine can use much larger samples, e.g.
typical of real batteries and chemical cells). The new
possibilities offered by D20 are now only being appreciated, and
the machine will be even more powerful with the new
monochromators at present under construction. Unfortunately, D20
is still very much a prototype instrument, and the continued
deterioration of it's microstrip elements during the year 1998,
probably due to insufficient cleaning during assembly, required a
long ( one year) shut-down and a major repair (see § 5a).
It is hoped that D20 will operate again in spring 2000.
D4 - This
instrument, installed on the hot source, is a liquids
diffractometer, rather than a powder machine. It is being
modernized with a bank of 9 high pressure He3
microstrip detectors (D4C project, see § 5a), which will
increase its efficiency by more than an order of magnitude,
making it a unique instrument for the study of small amorphous
samples, such as experiments using isotope contrast. It is
generally recognized that, even before this upgrade, D4 is the
best machine in its category in the world (this is largely due to
its exceptionnally high stability). Although one of the most
heavily demanded of the ILL instruments, D4 will however continue
to share a beam tube with IN1, and remain only 50 % scheduled.
D1A - This
"half CRG" is at present 50 % scheduled for ILL users (and,
up to 1998, 50 % CRG with the swiss community). It is the only
ILL diffractometer available for neutron strain scanning, a field
of increasing interest. Several industrialists (e.g. British
Aerospace, Volkswagen, EDF, etc...) have conducted paid beam time
experiments on D1A. There is currently a proposal by a consortium
group of five UK University groups to rebuild a dedicated strain
scanning instrument at ILL : this proposal is discussed within
the present review (see § 5b). D1A has produced some of the ILL's
most cited publications, but most high resolution Rietveld
refinement experiments are now made on D2B.
D1B - This
machine is now a 100 % CRG, run by a consortium associating the
Laboratoire de Cristallographie (CNRS, Grenoble, France) and the
CSIC/CICYT (Spain). D1B has produced more publications than any
other ILL machine (according to library records), and has been
heavily demanded for work in magnetism (structures and phase
transitions) and chemical kinetics. Crystallographic textures are
also studied on D1B (an Euler craddle is available). However, it
is supposed that the most demanding experiments in these fields
will be done in future on D20. D1B has been recently equipped by
CNRS with in situ thermogravimetry, allowing to
measure simultaneously diffraction diagrams and mass variations
under gas pressure (H2, N2, O2)
at elevated temperature.
c) Staff
During the
reactor cycles, the instruments are generally run 24 hours a day
by two ILL scientists and one technician; exceptions are : D4,
which has only one attached ILL scientist (D4 shares a beam with
IN1); D1A, which also has only one attached ILL scientist devoted
to the strain scanning activity (the second responsible left at
the ending of the swiss CRG); D1B, where the staff is supplied by
the CRG consortium (one scientist and one technician from CNRS,
Grenoble, and one scientist from Spain).
A few months ago,
the staff situation in powder and liquid diffraction was rather
bad, because the very experienced instrument responsibles of D2B
(Emmanuelle Suard) and D4 (Henry Fischer) were leaving ILL. The
situation could be stabilized for D2B by a staff scientist
contract for E. Suard, but not for D4. The departure of Henry
Fischer in August caused some difficulties for the D4C project (see
§ 5a); the latter is now supervised by Pierre Palleau, newly
appointed as an engineer, but with long experience on D4. It was
also possible to have an overlap between the departure of Henry
Fischer and the arrival of the new scientific responsible,
Gabriel Cuello, owing to the temporary help of Miguel Gonzalez (both
are experienced D4 users).
2. Statistics
a) Experimental
request and realization
The number of
scheduled experiments and the required and allocated beam time
for each of the reviewed instrument are given in Appendix 4 (the
CRG beam time is not included for D1A, and for D1B in 1997 and
1998).
Around 200
experiments are performed each year on the ILL powder instruments,
which corresponds to more than 25 % of the total number of ILL
experiments. Indeed, the average duration of an experiment on a
powder instrument is short, particularly on D2B : 2.5 days; it is
larger on D4 (4.5 days); it has increased on D1A (from 2.7 days
in 1996 to 4.4 days in 1998) because more stress experiments are
performed.
The ratio of
requested to allocated beam time varies from instrument to
instrument; on the average, it is 1.8, close to the average value
for ILL (1.9). It is particularly high (2.2) for the
diffractometer for liquids, D4, which operates only 50 % of the
year; D2B is also very demanded (2.0).
The loss of beam
time is small, generally between 1 and 6 % (exceptions : D20 in
1998 : 10 %, D4 in 1996 : 11 %).
ILL receives
approximately 300 individual users per year for experiments on
powder and liquid diffraction (see § 3).
b) Publications
The number of
publications arising from the 5 reviewed instruments are
summarized from 1996 in Table 3 of Appendix 4.
An analysis of a
set of 231 publications made in 1996 and 1997 showed that
somewhat more than half (132) are in reviews which may be
considered in the domain of physics (30 Phys. Rev.B, 8 PRL, 9
JMMM, 47 Physica B+C, 18 J. Phys. Condensed Matter, 3 Europhysics
Letters, etc...), and 40 % (86) in reviews related to
chemistry in a broad sense (including crystallography, metallurgy
and materials science : 11 J. Solid State Chem., 33 J. Alloys
& Compounds, 7 Chemistry of Materials, 6 Acta Cryst. + J.
Appl. Cryst., 3 J. Non Cryst. Solids, etc...).
The comparison of
the overall ILL publications over the past years shows that the
rate of publications in 1997 recovered the one before
refurbishment (516 in 1997 compared to 559 in 1990); for the
powder and liquid diffraction, recovery was already practically
attained in 1996 (122 publications in 1996 compared to 130 in
1990).
The delay between
experiment and publication varies considerably from one case to
the other; for the whole ILL, this is estimated to be 2 years.
The delay is usually shorter for powder experiments, with many
published within one year, but precise statistics are not
available.
The average
"success rate" of a powder diffraction experiment is
similar to the case of single crystal diffraction : about 50 %,
with some publications requiring more than one experiment (and
some experiments leading to several publications).
At the request of
the Scientific Council, a measurement of the impact of ILL
publications was made in 1998. The reference period is 1981-1997
inclusive, corresponding to 5085 papers, including work by both
ILL scientists and users.
63 publications
were found to be cited at least 100 times (for comparison, "normal"
papers are cited only 10-15 times), from which 11 were related to
the powder diffraction technique (see list in Appendix 3)
These include the
ILL's most cited publication (in 1990, by Cava et al, a Physica C
on charge transfer in oxide superconductors, 646 citations), and
also the most cited ILL publication since the reactor
refurbishment (in 1995, by Hwang et al, a Phys. Rev. Letters on
Giant Magnetoresistive materials, 218 citations) (see highlights,
§ 4a and Appendix 3).
In fact, 7 of
these 11 papers are related to structutal studies on the high Tc
cuprates, one on giant magnetoresistive perovskites, one on the
localization of benzene molecules in zeolithes, and two review
papers on powder neutron diffraction and on the structure of
liquid semiconductors. 6 of the 11 most cited papers correspond
to work on D2B, 3 on D1A, 1 on D4 and 1 on D1B.
3. Users
a) General
characteristics of the user community
The number of
different users on each instrument, from October 1994 to April
1998, are given below :
D2B |
D20 |
D4 |
D1A |
D1B |
471 |
246 |
150 |
266 |
419 |
The 4 powder
diffractometers, especially D1B and D2B, serve a large community,
about 3 times as great as on more specialised instruments. D4
only operates half time.
A more detailed
analysis of the user community for the period 1995-1998, and a
list of most frequent users for each instrument, are given in
Appendix 4.
The percentage of
"new" users in 1998 (i.e. which did not come since the
refurbishment in 1995) is 20-25 %.
b) Users
Survey
A questionnaire
was sent to 237 users. The 46 answers received ( 20 %) are
summarized in Appendix 2.
37 answers were
received from regular users (performing at least one experiment
per year), and 9 from occasional users. Generally, they
classify their work as fundamental research (31), but also as
materials characterization (20), applied research (7) and
technical development (7).
Surprisingly,
nearly half (20) did not work on other neutron sources. From the
others, many comments concern the complementarity between time-of-flight
and constant wavelength diffractometers (see § 6b).
The majority of
users found the instrument performance good or very good (30);
but several improvements are clearly required, in particular :
- of course solve
the detector problem on D20;
- install sample
changers at high or low T;
- improve the
electronics and data acquisition of D1B;
- install
oscillating radial collimators on D20 and D1B;
- on all
instruments, improve the software / user interface and in
particular the immediate visualisation of data.
All users
consider ILL powder diffraction instruments as essential for
their future research, especially if special sample environments
are developed. Super high flux is increasingly important (small /
short lived / diluted samples). The ultimate resolution of the
high resolution instrument must be improved (upgraded or new D2B).
A requirement of
the Solid State Chemistry community is that ILL should give more
time for short standard (at room temperature, in air) test or
characterization experiments, out of Scientific Council sessions.
4. Science
a) General
Neutron powder
diffraction (taken in its broad sense, i.e. including disordered
systems) covers an extremely wide range of scientific domains,
from very fundamental "academic" physics to industry
related problems. All five ILL instruments were at the origin of
important scientific achievements. A list of selected highlights
is given in Appendix 3.
D2B is
mostly involved in the detailed study of crystal and magnetic
structures, and their dependence with temperature, pressure, etc...,
by high resolution Rietveld refinements :
- nuclear and
magnetic structures, lattice-magnetic interactions (Jahn-Teller
distortions) in new oxides, including high Tc
superconductors and related compounds, giant magnetoresistive
oxides (see highlights), spin ladders, spin Peierls compounds;
- commensurate
and incommensurate magnetic structures, magnetic frustration in
rare earth, actinide and transition metal compounds;
- superionic
conductors : order-transitions, in-situ study of insertion, ...
- crystal
structure of clathrate systems, of fullerides, new metastable
high pressure forms of ice (see highlights),...;
- detailed
crystal structure, subtle phase transitions and H-bond studies in
molecular systems (hydroxides, sulfates, oxalates,.);
- insertion in
zeolites, site occupation in cements, interstitial solid
solutions and compounds, localisation of hydrogen or deuterium,
...
- structural
studies of quasi-crystals and approximants, decagonal phases.
D1A has
two domains of scientific activity : (i) powder structure
determinations and refinements, similar to those made on D2B, and
(ii) internal stress studies on materials of technological
interest, with the aim of predicting fatigue threshold and/or
validating finite element models.
Internal stress
studies in bulk materials include residual stress determination
in two-phase materials (e.g. metal matrix composites reinforced
by carbon or SiC fibers), in gradient materials, stress
relaxation during deformation, relation between residual stress,
grain shape and texture, ...
Many studies are
also made of residual stresses in interfaces (e.g. weldings) and
near surfaces (coatings, shot-peened materials, laser treated
surfaces,...).
D20 (and
to a less extent D1B) allows to study the same type of
problems than D2B when a very high counting rate is required (but
one is limited to medium resolution) : small samples, weak
reflection lines, fast measurements (required for example when
studying an unstable phase). But it gives also access to new
possibilities, in particular structural studies of thin films or
adsorbed layers, kinetic measurements and stroboscopic study of
cyclic phenomena.
The in situ
investigation and optimisation of synthesis or material
processing (e.g. industrial process for sintered magnets Nd2Fe14B),
and the study of kinetic reactions (dehydration or phase
transformations in cements, nitridisation, hydrogen absorption-desorption
in intermetallics,...) are new fields, initiated on D1B, and
where a breakthrough is now made possible by the high
intensity and the large position sensitive detector of D20.
Within its 2
years of operation, D20 has already allowed important scientific
achievements, such as :
- in situ study
of the crystallization of intermetallic amorphous ribbons,
showing the detailed sequence of phase transformations which
involve several metastable intermediate stages (at this occasion,
new intermetallic phases were discovered);
- extremely weak
incommensurate magnetic transitions;
- surface
corrosion studies of zircaloy (where the oxide film thickness was
as small as 1 µm);
- melting/freezing
of adsorbed water;
- orientational
alignment of plate-like particles under flow or electric field
and study of the relaxation processes by a stroboscopic technique.
D4 is
devoted to the determination ol local atomic arrangements and
structure factors in liquids and amorphous systems :
- study of the
many-body contribution to the interatomic potential in simple
monoatomic liquids;
- structure of
binary liquids, in particular under pressure, near the critical
point or in the supercritical conditions, in order to validate
numerical simulation models;
- structure of
complex liquids (aqueous and non-aqueous electrolyte solutions,
molten metal-salt mixtures,...);
- structure of
liquids in confined geometry (e.g. water in porous matrix,
interlayer water in clays);
- local order in
molten quasicrystals;
- local order in
amorphous solids and glasses (fast ion conductors, borate,
silicate, selenite or oxide glasses, ...), by the method of
isotopic substitution;
- structural
studies of nanocrystalline materials (carbon nanotubes,
nanocrystalline oxides,...).
Part of the
neutron beam time of D4 ( 10 %) is used in classical powder
diffraction, on Gd or other strongly absorbing rare earths, to
use the small wavelength, in particular for magnetic structure
studies.
b) Evolution
of subjects and scientific areas for future
Scientific
subjects studied by powder diffraction are evolving continuously
and rapidly.
In particular, a
large increase of residual stress studies, made essentially on D1A,
has been observed since the ILL refurbishment : from 28
days beam time (6 experiments) in 1995 to 85 days beam time (16
experiments) in 1998. Studies on GMR and charge-ordered
perovskites have "exploded" these last years and, for
example, occupied 30 % of the beam time on D2B in 1997 and
1998. On the other hand, neutron diffraction studies on surfaces
have decreased, people in this field go now preferentially to the
synchrotron.
As stated by one
user within his answer to the questionnaire, "whatever the
hot topic is in solid state chemistry, it is likely that powder (neutron)
diffraction will play a vital role in the (next) 20 years; one
has only to think of the topics that have come in and out of
fashion : ionic conductors, zeolites, high TC
superconductors, colossal magnetoresistive materials,....".
Scientific areas
for the future mentionned in the User's Survey are :
- in situ
preparation and kinetics,
- glaciology,
geology, palaeontology,
- structure and
phase transitions in molecular compounds relevant to
pharmaceutical research,
- defects in
structures,
- high pressures (at
least up to 60-70 GPa),
- materials of
industrial interest,
- nanostructured
systems : carbon nanotubes, liquids in confined geometries,...
5. Instrumentation
a) Microstrip
detectors
The rebuild of
the D20 microstrip detector is proceeding according to plan, with
users expected next May. Although the reasons for the destruction
of the previous detector are not entirely known, it is clear that
arcing due to poor contacts, interactions between high tension
supplies to adjacent plates, and insufficient clean glass and gas,
could all have contributed.
All three of
these problems have been adressed in the new detector, with good
plated contacts, modified electrode geometry, and reduced high
tension interaction between plates. The new plates have been
tested in a small prototype detector, and the complete set of
plates for D20 ordered.
These specific
problems are less important for the new D4C microstrip detectors,
since the modular design uses only one plate for each of the 9
detectors. Some delay has however been experienced because a few
of the plates delivered for D4 were below specification, and had
to be reordered.
Another
complication was the departure of the instrument responsible in
August; these staff problems have now been solved (see § 1c).
The new mechanics of D4C is at present being assembled, and start-up
of the new instrument is planned for May 2000.
b) The high
precision Strain Scanner project
D1A presents
unique advantages for strain scanning measurements : high flux
and high precision; the latter is due to the high angular
resolution of D1A, and to the coupled use of a radial collimator
and a position sensitive detector. But the present instrument has
also several drawbacks, in particular lack of space around the
instrument and fixed take-off angle.
Therefore a
consortium group of seven UK university groups, led by P. Withers
(Manchester Univ.), proposed to rebuild a new strain scanner
which should be one of the world leading instruments. The new
instrument would be installed on the thermal guide H22, behind D1B.
The major
scientific aim is to validate finite element calculations on
industrial devices. One will concentrate on the case of non-textured
samples of high crystalline symmetry, where one diffraction line
per phase gives the required information (more complex cases
should be studied on a time-of-flight instrument).
The eventual
opening of the instrument to crystallographic studies (for which
64 days beam time were allocated by ILL Scientific Council
Subcommittees in 1998) has not been decided yet.
The strain
scanner project was classified as high priority by the Powder
Diffraction workshop and the ILL Scientific Council. The funding
application to UK authorities is in progress.
c) Super-D2B
The ILL's high
resolution powder diffractometer D2B has now completed 15 years
service; it is still very demanded (requested-to-allocated beam
time ratio 2), has a high scientific production, but is
now competed by new instruments in other neutron sources, in
particular from ISIS. Moreover, the use of D2B in its highest
resolution mode, which is increasingly necessary with new
problems and small samples of new materials under extreme
conditions (e.g. subtle changes in the splitting of
superstructure lines), is limited by the relatively low flux and
long duration of experiments (typically 8 to 10 hours for a scan).
Super-D2B is
therefore a proposal to improve the efficiency of this instrument
by an order of magnitude. The project, presented in the frame of
the ILL Millenium Development Programme, contains two parts : (i)
a new high resolution set of detectors, and (ii) a new double-focussing
(horizontal and vertical) composite monochromator. High
resolution will be achieved in the horizontal plane with an array
of 128 mylar collimators. The necessary (lower) resolution in the
vertical direction will be obtained by charge localisation on 128
high pressure 300 mm linear wire 3He detectors. This
vertical resolution will be used to measure a large part of the
diffraction cone, rather than the usual small section in the
horizontal plane. Compared to the present instrument, the
detector solid angle will be increased by a factor 6.
The D2B upgrading
was given first priority by the Powder Diffraction Workshop and
the Subcommittees 5a and 5b (structures). Nevertheless, the
Scientific Council of april 1999 requested more precision on the
scientific case, and the Instrument Subcommittee raised questions
on the technical choice. Therefore, the decision has not been
taken yet.
d) Data
acquisition and software
The ILL Powder
Diffraction Workshop dedicated a session to data treatment and
software development (see Appendix 1). The main statements are
summarized below :
- In powder
diffraction, the software for data treatment is very much
developed. The reason is that the concerned community is quite
large and many people (including commercial companies) contribute
to that development. In what constant-wavelength neutron
diffraction is concerned, most of the structural work is largely
satisfied by the existing programmes.
- The specificity
of neutron diffraction makes that only some programmes, using the
Rietveld method (CCSL, FullProf, GSAS and RIETAN), have enough
features to handle complicated situations (in addition to the
conventional crystallographic problems) : anisotropic peak
broadening due to defects, spin correlation lengths or
crystallite size distributions, incommensurate magnetic
structures, rigid body and soft constraints refinements, multi-pattern
(treatment of heterogeneous data) capabilities, etc... Progress
is needed in more sophisticated cases : peak-shifts and asymmetry
due to some kind of defects, partial treatment of diffuse
scattering, incommensurate/composite crystal structures, complex
form factors of plastic crystals, etc...
- The free
distribution of the executable codes is very important. User-developer
feedback is the only way for correcting bugs and to compare the
relative performances for each particular problem. The role of
ILL in this respect is to contribute and support this kind of
activity.
- The development
of software for treating disordered materials is not so advanced
as those handling conventional crystallographic problems. The
concerned community may improve this situation.
- The improvement
of the present software should be concentrated in : documentation,
Graphical User Interfaces, simplifying the input files using a
command-oriented language and totally free format.
- An important
task that should be undertaken by the ILL is the development of
the software for handling the instruments and for in situ
preliminary data treatment : visualisation, integration, and
generation of data in appropriate formats. This is specially
important for new instruments producing a great amount of data (D20
for instance).
- The improvement
and/or the development of new diffraction software by scientists
take always longer than what was expected as starting. The
establishment of free Collaborative Diffraction Software
Development Groups (CDSDG) working with public source codes are
needed to improve and to increase the capabilities of present
software for data analysis.
6. Comparison
with other neutron and with synchrotron instruments
a) Comparison
with other constant wavelength neutron diffractometers
During the
workshop, instruments on present or future medium flux neutron
sources were presented and compared with ILL powder
diffractometers.
At LLB/Saclay (flux
5 times less than ILL) :
- G4.1 is analogous
to D1B, but on a cold neutron source : it has a comparable flux
with 800 cells instead of 400, and a slightly better
resolution than D1B at l = 2.4 Å; but the instrument lineshape
is not so good, and short wavelengths (1 - 1.5 Å) are not
available.
- 3T2 is analogous
to D2B, but of course with less flux; the resolution is
comparable to that of the "conventional" D2B, but less
than the "high resolution" D2B.
- G6.1 is a long
wavelength (l = 4.8 Å) instrument, largely devoted to high
pressures, and has no equivalent at ILL.
On SINQ (where
the flux is presently 20 times less than ILL) :
- DMC is a cold
neutron 2-axis instrument, with position sensitive multidetector;
it has a much lower flux than D1B, but a better background (due
to oscillating radial collimator).
- HRPT, a new high
resolution powder diffractometer, presently commissioning, has a
new 3He 1600 cells multidetector, and a high
resolution Dd / d = 2.5 10-3. It will be competitive
with D1A and D1B.
On FRM-2 (Munich),
where the flux should be near one half of that of the HFR-ILL, an
instrument of the type of D2B, with supermirror guide and 80
detectors, is foreseen.
In conclusion,
the best powder instruments on medium flux sources are far from D2B
and D20 in flux, but, owing to the progress in neutron optics,
become competitive with D1A and D1B. For liquids, the only
instrument on reactor source is 7C2 at LLB/Saclay, also on a hot
source; but D4 remains better, in flux and in scattering vector
range available (DQmax = 30 Å-1 on D4, 17
Å-1 on 7C2). These statements were confirmed by the
User's Review.
b) Comparison
with Time-of-Flight instruments
Powder
diffraction is one of the great successes of pulsed neutron
sources. The comparison between ILL and ISIS powder and liquid
diffraction instruments, in particular between D2B and HRPD, and
between D4 and SANDALS, was largely debated in the workshop and
in the answers to the questionnaire.
Generally, it was
found that time-of-flight (TOF) and constant wavelength
diffractometers (CWD) are complementary : each type of instrument
has advantages in certain circumstances, and both are often
needed for a full scientific coverage.
High
resolution diffractometers. Both leading instruments (D2B and
HRPD) are found excellent by users, with, in the average, similar
resolution and intensity. This can be understood because the
counting rate is proportional to the product of the detector
solid angle by the source solid angle; in CWD (compared to TOF
diffractometers), the latter is 10 times larger because of
the efficient focusing, but the former is 10 times smaller
because of mechanical constraints. HRPD gives access to a larger
q range (therefore to smaller d spacings) and has better
resolution than D2B at high q. Also, unlike D2B, HRPD has a
constant, synchrotron-like resolution Dq /q in all the q-range
accessible in back-scattering. However, obtaining low-q data and
merging them with high-q data is still a cumbersome and
unreliable procedure on HRPD. Therefore, D2B remains better for
magnetic studies, also in virtue of somewhat superior flux. D2B
has also a simpler peak shape and a better background. At ISIS, a
new high resolution diffractometer, OSIRIS, installed on the cold
source, is starting to operate : it should be much better than
HRPD for magnetic scattering and might compete with D2B.
Data corrections
and analysis are considered by most users as much more difficult
on spallation sources, because of complicated asymmetrical peak
shapes, difficulties in scaling overlapping parts of the pattern
(obtained on the different detector banks), and the necessity to
divide raw data by the incident spectrum, which must be
determined very precisely. But these difficulties can be overcome
by carefull work. Improvements to existing Rietveld-TOF software
(GSAS, CCSL) and the addition of the TOF option to the popular
FULLPROF package are expected to give a major contribution to the
TOF data analysis capabilities.
High flux
diffractometers. POLARIS (at ISIS) has higher resolution, but
lower counts and higher background than D20. But the new ISIS
instrument, GEM, equipped with 7 detector banks (10 times more
detecting angle than D20), should have a flux comparable to that
of D20. Because of the fixed geometry, TOF instruments are much
better adapted for high pressure crystallographic studies on
powders; at ISIS, pressures of 30 GPa at room temperature and of
15 GPa at 90 K have been obtained. (But magnetic structure
studies under pressure are performed on CWD, e.g. G6.1 in Saclay).
Diffractometers
for liquids. Although instruments on pulsed spallation
sources allow higher q values to be obtained (e.g. 40 Å-1
on SANDALS), CWD instruments and especially D4 are generally
preferred for diffraction studies on liquids, because of the much
better stability of source and detector (a precision of 5 10-4
on the measured cross-sections is required for studies involving
isotopic substitution) and the more easy data treatment. In two
cases, SANDALS was preferred to D4 : (i) larger flux in a
specific q range (0.3 - 3 Å-1), and (ii) better for H
substitution. But TOF diffractometers for liquids cannot be used
for rare earths (because of resonances), and more generally are
more difficult for absorbing systems. A lot of work has still to
be done to improve data treatment software for disordered
materials studied on pulsed spallation sources.
c) Neutrons
versus Synchrotron Radiation in Powder Diffraction
A session was
devoted to this subject during the workshop.
The
characteristics of high energy synchrotron radiation (parallel
beam optics, vertical focusing) allow considerable advantages in
powder diffraction : very small instrumental linewidth (e.g. D2qFWHM
= 0.006° on BM16 at the ESRF) and very accurate scattering
angles (± 1 second on BM16), well defined lineshapes, high
statistics, weak absorption,... Kinetic experiments can be
performed at the time scale of 0.1 s, but the demand is
not very high. Damaging of the sample by the beam is generally
not a big problem in the case of high energy X-rays, because the
absorption is small.
In conclusion,
neutrons and synchrotron radiation are complementary : very
generally speaking, if X-rays are better than neutrons for
structure determination, neutrons are better than X-rays for
structure refinement, in particular for obtaining precise site
occupancies and precise atomic positions of light elements in the
presence of heavy elements (the statistics of published
structural work with Rietveld refinement give 3276 cases with
neutrons, 2557 with conventional X-rays and 126 with synchrotron
X-rays). This is due to several factors : the weak neutron-matter
interaction, the easiness of corrections, the independence of
neutron scattering length versus q.
X-rays are better
for small samples (although the modelisation of granularity and
of preferred orientation may be difficult), and neutrons are
better for large samples as required for example in real-time
diffraction studies of chemical or electro-chemical processes. A
number of scientific problems call for a simultaneous use of both
radiations, and we expect to see more and more coupled neutron -
synchrotron radiation structural studies.
Neutrons are of
course unique for magnetic structure determination. Synchrotron
radiation is leading in the field of high pressures, because of
the smaller samples : phase diagrams and structures could be
studied at pressures as high as 180 GPa (in comparison to Pmax
= 40 GPa with neutrons in Saclay), but some aspects cannot be
studied with X-rays : magnetic structures, precise structural
informations on H and D, many aspects of diffuse scattering.
Because of the
weak absorption of high energy X-rays, and the high accuracy on
scattering angles, synchrotron radiation offers very attracting
perspectives in the field of strain scanning; but many difficult
aspects have to be overcome, due in particular to the needle
shape of the gauge volume.
Concerning
diffraction by liquids, X-rays allow studies in a large q domain
for elements ranging from Z = 30 to 50. But there is never
enough contrast to obtain partial structure factors in diatomic
liquids by using the anomalous effect : the only technique at
present is neutron scattering with isotopic substitution.
7. Conclusion
: the powder diffraction instrument profile of ILL
Powder
diffraction (including conventional X-rays, synchrotron radiation
and neutrons) is a technique with increasing applications in many
fields of Science. It is one of the first techniques to be
applied to new materials, which are often available as impure
samples and in small quantities.
If the powder and
liquid ILL diffractometers were the best in their categories
since the origin, the progress in neutron optics has allowed some
medium source instruments (present or future) to become
competitive with D1A and D1B. Moreover, the great success of
spallation sources in the field of powder neutron diffraction (see
§ 6b) has challenged the supremacy of ILL in this field (with
the exception, surprisingly, of the diffractometers for liquids).
Therefore, the upgrading and modernization of the ILL powder
diffraction instruments is a priority, in order to optimize the
use of the high flux source.
The ILL powder
diffraction instrument profile for the future was largely
discussed during the workshop. It was generally agreed that the
minimum required is :
- a "fast"
instrument for kinetics (with fixed multidetector, medium / good
resolution) : it was D1B, it is now (and it will be) D20;
- a "high
resolution" instrument for structures : it was D1A, it is
now D2B, it should be in the future super-D2B (or a new
instrument) with very high resolution.
They should be
accompanied by two more specialized instruments :
- a diffractometer
for liquids, with fixed short wavelength neutrons, installed on a
hot source : it was D4, it will be D4C;
- a high resolution
strain scanner.
With this port-folio,
it may be remarked that the number of "true" powder
diffractometers at ILL is smaller than at ISIS (4) and at LLB (4).
Although their
achievements are now catched up by some medium source
diffractometers, it was generally agreed that D1A and D1B will
still remain usefull instruments for the future, especially for
demanding sample environments (low and high temperatures, high
pressures, in situ electrochemical experiments,...). In
particular, it is recommended that the 50 % scheduled D1A
instrument should remain operational at least up to the repair of
D20 and the upgrade of D2B.
According to
several users and speakers at the Workshop, there is a gap in the
instrument suite described above : a high intensity instrument
for structure resolution, with good Rietveld refinement (i.e.
intermediate between D20 and D2B) is missing; this requires a
high resolution option on D20, with focusing Ge monochromator and
large take-off angle.
Other demands are
:
- a powder
diffractometer on cold source for magnetic structure studies; but
D16 could partially fulfill this role;
- a high
resolution powder diffractometer on hot source with fixed short
wavelength, for good structural refinements at high q, precise
determination of Debye-Waller factors, study of disorder (diffuse
scattering), etc... ; but in the present state of the art, it
would be difficult to have a good monochromator with high take-off
angle.
For the future,
ILL should think on what could be its best high resolution powder
diffractometer. It was in particular proposed (P. Radaelli) to
consider the case of a TOF machine installed on a reactor,
running in energy dispersive mode; such an instrument would
present several advantages, compared to a TOF on spallation
source (symmetrical line shape), or to a CWD (fixed geometry,
very large detector solid angle, no higher energy contamination).
One should also
develop the use of polarized neutrons; satisfactory tests of He3
filter and of CRYOPAD (3-dimensional polarization analysis) have
recently been made on D1B.
Charles de NOVION
Chairman of ILL
Powder Diffraction Instruments Review
With the
collaboration of J.C. GOMEZ-SAL, P. RADAELLI,
J. RODRIGUEZ-CARVAJAL,
A. HEWAT and P. CHIEUX
Appendix
3 : HIGHLIGHTS AND IMPACT OF ILL PUBLICATIONS
Most
cited powder and liquid diffraction ILL publications
Are indicated
the ranking in the overall ILL impact list, the number of
citations in the reference period 1981-1997 inclusive, the
instrument (in parenthesis), the authors, the year of publication
(in parenthesis), the precise reference and the title of the
paper. Only publications bearing the ILL name are
considered. (For an analysis of all 5085 ILL papers published
between 1981 and 1997, please refer to the ILL citation page http://www.ill.fr/dif/citations/).
N°1 - 646 (D2B)
Cava, R.J., Hewat, A.W., Hewat, E.A., Batlogg, B., Marezio, M.,
Rabe, K.M., Krajewski, J.J., Peck, W.F. and Rupp, L.W. (1990)
Physica C. 165, 419. "Structural anomalies oxygen
ordering and superconductivity in oxygen deficient Ba2YCu3Ox".
N°4 - 466 (D1A)
Capponi, J.J., Chaillout, C., Hewat, A.W., Lejay, P., Marezio, M.,
Nguyen, N., Raveau, B., Soubeyroux, J.L. and Tholence, J.L. (1987)
Europhysics Letters. 3, 1301. "Structure of the
100 K superconductor Ba2YCu3O7
between 5-300 K by neutron powder diffraction".
N°10 - 218 (D2B)
Hwang, H.Y., Cheong, S.W., Radaelli, P.G., Marezio, M. and
Batlogg, B. (1995) Physical Review Letters. 75, 914.
"Lattice effects on the magnetoresistance in doped LaMnO3".
N°18 - 195 (D1A)
Fitch, A.N., Jobic, H. and Renouprez, A. (1986) Journal of
Chemical Chemistry. 90, 1311. "Localisation of
benzene in sodium-Y zeolite by powder neutron diffraction".
N°19 - 191 (D2B)
Kaldis, E., Fischer, P., Hewat, A.W., Hewat, E.A., Karpinski, J.
and Rusiecki, S. (1989) Physica C. 159, 668. "Low
temperature anomalies and pressure effects on the structure and Tc
of the superconductor YBa2Cu4O8
(Tc = 80K)".
N°28 - 169 (D2B)
François, M., Junod, A., Yvon, K., Hewat, A.W., Capponi, J.J.,
Strobel, P., Marezio, M. and Fischer, E.W. (1988) Solid State
Communications. 66, 1117. "A study of the Cu-O
chains in the high Tc superconductor YBa2Cu3O7
by high resolution neutron powder diffraction".
N°45 - 129 (D1A/B)
Rodriguez-Carvajal, J. (1993) Physica B. 192, 55. "Recent
advances in magnetic structure determination by neutron powder
diffraction".
N°48 - 125 (D2B)
Bordet, P., Capponi, J.J., Chaillout, C., Chenavas, J., Hewat, A.W.,
Hewat, E.A., Hodeau, J.L., Marezio, M. and Tholence, J.L. (1988)
Physica C. 156, 189. "A note on the symmetry and
Bi valence of the superconductor Bi2Sr2CaCu2O8".
N°49 - 125 (D1A)
Roth, G., Heger, G., Renker, B., Pannetier, J., Caignaert, V.,
Hervieu, M. and Raveau, B. (1988) Physica C. 153-155, 972.
"Crystallographic study of the tetragonal high-Tc-superconductor
YBa2(Cu0.95Fe0.05)3O7".
N°58 - 105 (D4)
Enderby, J.E. and Barnes, A.C. (1990) Reports on Progress in
Physics. 53, 85. "Liquid semiconductors".
N°60 - 102 (D2B)
Hewat, A.W., Capponi, J.J., Chaillout, C., Marezio, M. and Hewat,
E.A. (1987) Solid State Communications. 64, 301. "Structures
of superconducting Ba2YCu3O7-d
and semiconducting Ba2YCu3O6
between 25 degrees C and 750 degrees C".
List
of highlights for each instrument
D1A
Capponi, J.J.,
Chaillout, C., Hewat, A.W., Lejay, P., Marezio, M., Nguyen, N.,
Raveau, B., Soubeyroux, J.L. and Tholence, J.L. (1987).
Europhysics Letters 3, 1301.
"Structure
of the 100 K superconductor Ba2YCu3O7 between
5-300 K by neutron powder diffraction". - One of the 10 most
cited papers in all the science in 1988, revealing the layer
structure of the 90 K superconductor (X-rays simply showed a
disordered perovskite); this and other neutron powder work
stimulating a successful search for new layered high-Tc superconductors.
Medarde, M.,
Lacorre P., Conder, K., Fauth, F. and Furrer, A. (1998). Physical
Review Letters 80, 2397.
"Giant 18O
- 16O isotope effect on the metal-insulator transition
of RNiO3 perovskite (R = rare earth)".
Kraemer, K.,
Guedel, H.U., Roessli, B., Fischer, P., Doenni, A., Wada, N.,
Fauth, F., Fernandez-Diaz, M.T. and Hauss, T. (1999). Physical
Review B R3724.
"Non-collinear
two- and three-dimensional magnetic ordering in the honeycomb
lattices of ErX3 (X = Cl, Br, I)".
Some of the first
work establishing the interest of high resolution neutron
diffraction for internal stress measurement (Harwell group and G.A.
and P.J. Webster), leading to the UK/ILL proposal for a dedicated
stress machine.
D1B
Charrier, B.,
Ouladdiaf, B. and Scmitt, D. (1997). Physical Review Letters 78,
4637.
"Observation
of Quasimagnetic Structures in Rare-Earth-Based Icosahedral Quasi-Crystals
- a first demonstration of ordered magnetism in such materials".
Alonso, J.A.,
Garcia-Munoz, J.L., Fernandez-Diaz, M.T., Aranda, M.A.G.,
Martinez-Lope, M.J. and Casais, M.T. (1999). Physical Review
Letters 82, 3871.
"Charge
disproportionation in RNiO3 perovskites : simultaneous
metal-insulator and structural transition in YNiO3"
- two different Ni moments were found with D1B data, while D2B
data showed the charge modulation.
Alonso, J.A.,
Martinez, J.L., Martinez-Lope, M.J., Casais, M.T. and Fernandez-Diaz,
M.T. (1999). Physical Review Letters 82, 189.
"Room
temperature magnetoresistance and cluster-glass behavior in the
Ti2-xBixMn2O7 (0 = x
= 0.5) pyrochlore series".
Many early papers
establishing real-time chemistry and electro-chemistry as a new
technique.
D2B
Cava, R.J., Hewat,
A.W., Hewat, E.A., Batlogg, B., Marezio, M., Rabe, K.M.,
Krajewski, J.J., Peck, W.F. and Rupp, L.W. (1990). Physica C 165,
419.
"Structural
anomalies oxygen ordering and superconductivity in oxygen
deficient Ba2YCu3Ox".
The most cited
ILL paper ever, introducing the concept of charge reservoirs in
high Tc superconductors.
Hwang, H.Y.,
Cheong, S.W., Radaelli, P.G., Marezio, M. and Batlogg, B. (1995).
Physical Review Letters 75, 914.
"Lattice
effects on the magnetoresistance in doped LaMnO3"
- a study of charge ordering effects associated with Giant
Magneto-Resistive materials; several other D2B papers have been
widely cited, including the work on the stripe versus Wigner
crystal controversy - see also D1B.
Kasakov, S.M.,
Chaillout, C., Border, P., Capponi, J.J., Nunez-Regueiro, M.,
Rysak, A., Tholence, J.L., Radaelli, P.G., Puttin, S.N. and
Antipov, E.V. (1997). Nature 390, 148.
"Discovery
of a second family of bismuth-oxide-based superconductors".
Lobban, C.,
Finney, J.L., Kuhs, W.F. (1997). Nature 391, 268.
"Discovery
of a new phase of ice".
D20
Koza, M., Schober,
H., Toelle, A., Fujara, F. and Hansen, T. (1999). Nature 397,
660.
"Formation
of ice XII at different conditions of temperature and pressure".
Caciuffi, R.,
Mira, J., Rivas, J., Senaris-Rodriguez,, M.A., Radaelli, P.G.,
Carsughi, F., Fiorani, D. and Goodenough, J.B. (1999).
Europhysics Letters 45, 399.
" Transition
from itinerant to polaronic conduction in La1-xSrxCoO3
perovskites" (using both D20 and D2B).
Brown, A.B.D.,
Clarke, S.M. and Rennie, A.R. (1998). Progr. Colloid Polym. Sci. 110,
80.
"Shear
induced alignment of kaolinite. Studies using a diffraction
technique" - Application of stroboscopic texture analysis to
study dynamic flow behaviour of particles in suspension.
Kohlmann, H.,
Gingl, F., Hansen, T. and Yvon, K. (1999). Angew Chem. Int. Ed. 38,
2029.
"The first
determination of Eu-H distances by neutron diffraction on the
novel hydrides EuMg2H6 and EuMgH4".
An application of very short wavelengths to solve crystal
structures of strongly absorbing rare earth samples (natural
isotopes) - only possible with a very high flux machine.
D4
Celli, M., Magli,
R., Fischer, H.E., Frommhold, L. and Barocchi, F. (1998).
Physical Review Letters 81, 5828.
"Quantum
mechanical effects on the static structure factor of pairs of
orthodeuterium molecules".
Simonet, V.,
Klein, H., Bellissent, R., Hippert, F. and Audier, M. (1998).
Physica B 234, 594.
"Magnetism
and local order in AlPdMn liquid alloys" - The first and
most successful high-T furnace experiment at D4, and nicely
linking the liquid structure (having icosahedral clusters) with
the Mn magnetic moment, using NMR and D7 results as well.
Barnes, A.C.,
Lague, S.B., Hamilton, M.A., Fischer, H.E., Fitch, A.N. and
Dooryhee, E. (1998). J. Phys. Condensed Matter 10, L645.
"A
determination of the partial structure factors of liquid Tl-Se
using combined X-ray and neutron diffraction".
Burian, A., Dore,
J.C., Fischer, H.E., Sloan, J. and Szczygielska, A. (1999). Proc.
SPIE 3725, 107.
"Structural
studies of carbon nanotubes by wide-angle neutron scattering".
Appendix
4
STATISTICS
ON EXPERIMENTS, PUBLICATIONS AND USERS
Table 1 : Number of scheduled experiments
Year |
1998 |
1997 |
1996 |
|
|
|
|
D2B |
74 |
81 |
62 |
D20 |
57 |
31 |
- |
D4 |
22 |
22 |
20 |
D1A* |
30* |
29* |
47* |
D1B* |
28* |
45* |
80 |
|
|
|
|
Total |
211 |
208 |
209 |
|
|
|
|
Total
ILL |
749 |
760 |
791 |
* CRG instruments are marked with an
asterisk. Experiments on CRG beam time are not included.
Table 2 : Requested beam time (days)
(allocated beam time is indicated in italics
between parenthesis)
Year |
1999 |
1998 |
1997 |
1996 |
|
|
|
|
|
D2B |
341 (165) |
273 (175) |
348 (188) |
373 (175) |
D20 |
28 (0) |
213 (160) |
108 (95) |
- |
D4 |
184 (85) |
203 (97) |
194 (92) |
202 (79) |
D1A* |
213 (97) |
251 (131)
* |
163 (124)
* |
127 (125)
* |
D1B* |
194 (120)* |
89 (90)
* |
218 (110)
* |
346 (197) |
Total |
960 (467) |
1029 (653) |
1031 (609) |
1048 (576) |
|
|
|
|
|
Total
ILL |
8418 (4581) |
8894 (4539) |
8967 (4655) |
8240 (4459) |
* CRG instruments are marked with an
asterisk. Proposals for CRG beam time are not included.
Table 3 : Number of publications *
Year |
1998 |
1997 |
1996 |
TOTAL |
|
|
|
|
|
D2B |
21 |
52 |
34 |
107 |
D20 |
10 |
6 |
4 |
20 |
D4 |
12 |
17 |
10 |
39 |
D1A |
22 |
22 |
19 |
63 |
D1B |
58 |
69 |
55 |
182 |
|
|
|
|
|
Total |
123 |
166 |
122 |
411 |
|
|
|
|
|
Total
ILL |
|
516 |
314 |
|
* includes non-refereed and non published
work, as included in the ESRF / ILL library
Analysis
of the user community for each instrument
The analysis
concerns the experiments performed between 1995 and 1998
inclusive (4 years). The classification considers the first
proposer, not the research group.